This invention includes a shift mechanism for transverse indexed movement of a tufting machine needle bar to extend the pattern making capabilities of a tufting machine, reduce noise and eliminate the dangerous work environment associated with hydraulic or pneumatic shifting systems.
In the production of tufted fabric it is known to jog or shift the needle bar in its longitudinal direction transversely across the tufting machine relatively to the backing material in order to create various pattern effects, to break up the unattractive alignment of the longitudinal rows of tufts and to reduce the effects of streaking which results from variations and colorations of the yarn.
Various devices have been proposed and are in use for controllably applying a step-wise force to the needle bar of a tufting machine in accordance with a pattern. Such needle shifting or stitch placement drives conventionally fall into two categories, cam driven and programmable shifting.
In the cam driven type a rotating plate cam is driven directly from the tufting machine main shaft, and engages the needle bar to effect the required displacement. The second category, the programmable type, is powered by a hydraulic or pneumatic drive, or driven mechanically through some form of programmable indexing device whereby a ram is drivingly engaged with the needle bar so as to effect the required displacement thereof. Examples of such drives are illustrated in U.S. Pat. Nos. 3,964,408 and 3,972,295, which utilize pawl and ratchet devices, U.S. Pat. Nos. 4,010,700 and 4,392,440 which utilize indexing devices and 4,173,192 which uses a hydraulic actuator.
Because of the greater reliability, simplicity and lower cost of a cam drive system, the cam driven needle bar shift remains the primary drive for supplying controlled step-wise force to the needle bar in accordance with the pattern information on the periphery of the pattern cam. Examples of such needle shifting devices are disclosed in U.S. Pat. Nos. 3,016,380, 3,934,524 and 4,445,447.
In the conventional cam driven needle bar shift apparatus, the cam acts on cam followers connected through drive rods and the like to the needle bar. The cam is rotatably driven through proper reduction apparatus from the main shaft of the tufting machine and rotates at a constant speed in synchronization with the movements of the needles, the hooks or loopers and the backing material. The cam serves to drive the needle bar in its longitudinal direction during that portion of the machine cycle when the needles are above and out of engagement with the backing material in which the stitches are to be formed so as to avoid interference between the needles and the needle plate or other portions of the machine. The needles are clear of the backing only during a small portion of the cam circumference so that only this portion of the cam circumference is available for controlling the transverse needle bar movement while the remaining portion of the cam circumference is of a constant radius and merely idles the needle bar in place. Thus, the number of needle bar movements for a given cam is limited, and the stitch pattern repeat is similarly restricted due to the relationship between the "dwell" time, i.e., the period within a machine cycle when the needles are engaged with the backing material and no longitudinal shift of the needle bar can occur, and the "displacement" time, when the needles are withdrawn from the backing and the needle bar is jogged.
Typically, the needle bar is shifted or jogged laterally across the machine during approximately 120.degree. to 180.degree. of the needle bar reciprocation cycle so that the "displacement" time using a conventional cam driven shifter is approximately 33 percent to 50 percent of the machine cycle and of the circumference of the cam, with the remaining 50 to 67 percent of the cam circumference and machine cycle being an idle surface or the "dwell" time. Thus, for a major part of its rotation the cam is precluded from affecting shifting of the needle bar.
If the surface of the cam is divided into sectors equal in number to the number of stitches in the pattern, the angular distance from a point in one sector to a similarly disposed point in an adjacent sector is the angle the cam must rotate for each revolution of the tufting machine main shaft and for each cycle of the needle bar. Because of this, and because of the small surface available for a follower to ride upon each sector of a practical sized cam, the number of sectors into which the cam may be divided, and hence the number of stitches in a pattern produced by the cam, is limited. Moreover, because of the small amount of time available for needle bar displacement, coarse cam profiles must be utilized for the displacement step, thereby giving rise to problems of inertia in relation to the needle bar and militating against accurate and smooth needle bar movement. Because of the abrupt changes in the shape of the cam surface to produce the required abrupt directional reversals of the movement of the needle bar as the cam rotates, problems arise with regard to ensuring that the cam follower runs smoothly on the cam surface and it is difficult to achieve satisfactory pattern control in the case of high speed tufting machines. Additionally, the need for rapid transition between the "dwell" and "displacement" portions of the total cam profile require that cam followers of relatively small size be utilized, which in itself gives rise to further problems relating to dynamic response characteristics. Such systems are inherently noisy in operation due to the clicking sounds produced by the collisions of the cam follower with the cam pattern changes. The cam is limited to a relatively small number of shifts for each pattern. To change patterns the cam must be changed, requiring the machine to be out of production while the pattern cam is changed.
The limitations of a cam shifting means are overcome in part by programmable shifting systems but such systems also involve a new set of problems. Hydraulic and pneumatic systems operate under high fluid pressures which eventually leak and fail due to loss of fluid pressure. Pressure failure during a bar shift may result in a partial shift, causing the needles to contact the loopers or needle plate, often requiring replacement of all loopers and needles and rethreading of all needles. A large commercial tufting machine will often carry over 1,000 needles per needle bar, and many machines carry two independent bars. On these large systems a needle bar crash may result in the loss of several thousand dollars in replacement of bent or broken needles and loopers, as well as the loss of one or more full days of production from the damaged machine. Leaking hydraulic fluids also present a cleanliness problem, and safety, health and environmental problems for the machine operators. Pneumatic systems are noisy, and high pressure gas lines also present safety problems for the operator.
Ratchet and pawl type shift mechanisms are complex, noisy and limited in the range of patterns that can be programmed. Very few, if any are currently in commercial use. Even in the widely used hydraulic shifted machines, the maximum transverse shift range in large scale commercial tufting machines is limited to about three inches of total needle bar displacement, and much less shift capacity is normally available in com or ratchet and pawl type machines.
The shifting range is limited in hydraulic shifting machines by the amount of hydraulic fluid a particular system can supply at full pressure to drive the actuator. In hydraulic systems the valve response is proportional to the control signal, but the response is nonlinear causing over shift or under shift and requiring careful control circuit tuning to avoid stability problems or poor dynamic response. These factors result in a limiting of the practical shifting range of hydraulic or pneumatic systems to about 1.5 inches right and left of center, or a total shift range of about 3.0 inches.